This invention relates to a phase correcting method in a magnetic resonance imaging system and a device for realizing the same and in particular to a method for correcting phase distortions in tomographic data obtained in a tomographic system for a living body utilizing magnetic resonance phenomena and a device for realizing the same.
In general, in a magnetic resonance imaging system (hereinbelow abbreviated to MRI system) a living body is irradiated with a static magnetic field, a radio-frequency magnetic field and gradient magnetic fields and these magnetic fields fluctuate in position and in time with respect to the magnetic fields, with which the living body is to be irradiated ideally. Because of these fluctuations data of each pixel in a tomographic image detected by means of an MRI system contain phase distortions.
Heretofore, as a method for correcting phase distortions depending on the position in a tomographic image obtained by means of an MRI system there is known a method, by which phase distortions are obtained previously by calculation, starting from an image obtained by imaging a uniform body called a phantom under the same conditions as those used for a tomographic imaging by means of the MRI system and phase distortions in a tomographic image are corrected by using the calculated phase distortions thus obtained.
Since the phase distortions fluctuate in time and further they fluctuate also depending on the imaging procedure, the position of the tomographic image, etc., in order to correct the phase distortions with a high precision, there are problems that it is necessary to obtain frequently tomographic images of the phantom stated above, which takes a lot of time, and that operations of the MRI device are complicated.
As a method for correcting the phase distortions, using only data of obtained tomographic images, a method for correcting them by operations of absolute values is widely utilized. This method is disclosed e.g. in Ahn et al. "A New Phase Correction Method in NMR Imaging Based On Autocorrelation And Histogram Analysis" IEEE Transactions on Medical Imaging, Vol. MI-6, No. 1, 1987, pp 32-36. This method had a problem that, in the case where an imaging procedure, by which images where there exist originally mixedly positive and negative data are obtained, are used, such as the inversion recovery method (IR method), sign information is lost by the operations of absolute values.